The invention relates to aqueous correction fluids.
Correction fluids are used for correcting typed, handwritten or photocopied markings on paper. Generally, correction fluids are applied to paper surfaces in liquid form and then allowed to dry to form a film which effectively covers erroneous markings on the surface and which can receive a corrected marking.
Aqueous correction fluids typically include a pigment, e.g., titanium dioxide, a latex binder, which is usually a copolymer emulsion. Ethylene vinyl acetate (EVA) is the preferred latex binder/copolymer emulsion, since it minimizes bleed of underlying markings to which the fluid is applied and imparts other advantageous properties to the fluid.
Traditionally, correction fluids have also contained volatile organic solvents as freeze-thaw stabilizers. These fluids generally exhibit good freeze-thaw stability, i.e., the fluids are better able to resist coagulation after a number of freeze-thaw cycles. Coagulation is the irreversible agglomeration of particles originally dispersed in the latex. Volatile organic compounds (VOC), e.g., alcohols prevent coagulation of correction fluids by depressing the freezing point of water.
For environmental and safety reasons, it would be beneficial to eliminate all VOC's from correction fluids. However, with some fluids, reduction or elimination of VOC's can lead to freeze-thaw instability, particularly for those fluids containing inherently freeze-thaw unstable emulsions, most notably EVA emulsions. Without additional stabilization, aqueous correction fluids containing EVA emulsions typically coagulate. Therefore, these types of fluids are generally considered impractical for commercial use, as freeze-thaw conditions are frequently encountered in shipping and storage of correction fluids.
One solution to this problem is to use latex binders/polymer emulsions which are freeze-thaw stable. Unfortunately, most commercially available polymer emulsions which have good freeze-thaw stability tend to produce more bleed, when used in correction fluids, because of the amounts and types of surfactants/colloids used to stabilize them.